At the end of Q3 2008, Nielsen estimates that there are 3.6M mobile subscribers Apple’s iPhone (U.S.-based over 13), giving the device a 3% market share in the mobile business. Growth seems evident as one in five subscribers (21%) who intend to upgrade their mobile device in the next 12 months say they’ll consider purchasing an iPhone next – up from just 15% last year. In addition to Apple and AT&T’s combined 36M advertising campaign, what may be driving this growth is unmatched customer satisfaction. In Q3 2008, 89% of …